Picture transmission



P. c. GARDINER 1,950,171

PICTURE TRANSHIYSSION Filed Dec. 16. 1930 Invehtor: Paul C. Ga'bdinefi by 1 H is Attorney.

Patented Mar. 6, 1934 PATENT OFFICE PICTURE TRAN SMISSION Paul C. Gardiner, Seotia, N. Y., assignor to General Electric Company, a corporation of New York Application December 16, 1930, Serial No. 502,747-

6 Claims. .(Cl. 1785) My invention relates to the transmission of shaded pictures. When the methods heretofore employed for the transmission of black and white pictures or simple modifications thereof have been attempted for the transmission by radio of shaded pictures, various difiiculties have'been encountered. For example, the method of sending by turning on the transmitter varying amounts for various shades of the picture is successful only when fading does not exist. The method of transmitting the shades of the pictures by efiecting variations in frequency of the carrier necessitates extremely close tuning at the receiver unless a wider frequency band is available than that usually allotted. Moreover, widening of the frequency band greatly increases the problem at the transmitter of producing the desired frequency variations. It is the object of my invention to provide an improved method of 20 transmitting shaded pictures and improved apparatus for carrying out the method which is simple and eiiicient in character, and which in use avoids the difliculties heretofore encountered.

My invention will be better understood from the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

Referring to the drawing, Fig. 1 represents 30 diagrammatically picture transmitting apparatus embodying my invention; Fig. 2 illustrates the wave form of the currents in various parts of the apparatus of Fig. 1; and Fig. 2 is a specimen of the shading of the received picture.

35 In illustrating my invention 1 have chosen to show at 1 a well known form of scanning apparatus comprising a rotatable optical system which includes an objective lens and a prism 2 by which the light from successive unit areas of 40 the picture 3 is directed along the axis of rota tion, as shown by the dot and dash line 4, into the photo-electric cell 5. Between the prism 2 and the cell 5 is the chopper wheel 6 which is rotated at a uniform rate and whose teeth determine the frequency of the transmitted impulses and hence the spacing or pitch of the received impressions which make up the picture. The

output current of the cell 5 is amplified by the of which are arranged to be'heated by currentreceiyed from the transformer 12. The plate circuits o1! devices 10 and 11 connect through the transformer 14 with the grid circuits of the electron discharge devices 16 and 1'7. The plate circuits of the latter devices are connected together in order to rectify the current received at therefrom and are fed by the same plate battery 18 through resistance 20. The potential difference across the resistance 20 is amplified by the electron discharge direct current amplifying device 22 whosegrid and filament connect 5 respectively with the opposite ends of the resistance 20. The plate circuit of the direct current amplifier 22 is shown connected with the radio transmitter 23, having the antenna 24. The transmitter 23 is so constructed that it oper- 7 ates when the amplifier 22 is not operated and is inoperative or cut off' when the amplifier is operated. It will be understoodthat the picture signals may be transmitted to a distant point by other means than by radio if desired.

The shape of the teeth of the chopper wheel 6 and the shape of the light beam traversing this wheel are so related that the wave shape of the impulses received from the photo cell and supplied to the grids of the devices 10 and 11 is subgo stantially as shown at in Fig. 2 where the wave is shown as having substantially straight sides. As a result of the amplification of this wave by the devices 10 and 11, the wave is rendered'scrnewhat concave, as shown, for example, at 31, which for convenience is arranged in Fig. 2 beneath the output circuit of devices 10 and 11. The curvature of the wave is still further increased by the devices 16 and 17, and as a result of the circuit arrangement the wave is rectified as shown at 32. While I have described the concaving of the wave 31 as due to the effect of devices 10 and 11, this effect may, if desired, be produced by suitably shaping; the teeth of the chopper, the beam of light intercepted by the chopper, or both. I have found that the resulting wave such as shown at 32 has a form which approximately follows the equation Hence, that portion b lying between the points of intersection c and d of the line a'parallel with the :1: axis of the curve is approximately inversely proportional to the amplitude of the wave. In illustrating the waves 30, 31 and 32 no attempt has been made to show them iii-their proper proportions. t

The resistance 20 in the plate circuit of devices 10 and 1'! is or such a value that whenever the 1 current therein is at a value corresponding to a, the potential difference across the resistance 20 is just sufiicient to operate the amplifier 22. Below that value the amplifier is not actuated and for all amounts slightly above that value the amplifier is actuated to its full extent, at which times as explained above the transmitter 23 is cut off.

In the operation of this apparatus the variations in shade of the successive unit areas scanned of the picture 3 cause corresponding variations in amplitude of the waves 30, 31 and 32. By reason of the shape of the waves 32 variations in amplitude of these waves produce corresponding variations in the length of time indicated by the distance b that the amplifier 22 is not operating and hence the length of time that the radio transmitter 23 is operating. As a result signals are transmitted from the radio transmitter which have a uniform frequency determined by the speed of the chopper 6, and which vary in length or duration in accordance with the shade of the successive unit areas of the picture being transmitted.

In Fig. 3 I have shown, by way of example, three specimens of shading of the received picture. That represented at A would correspond to a light portion of the transmitted picture; that represented at B would correspond to a medium gray portion; and that portion shown at C would correspond to a dark portion of the picture. It will be understood that these three portions are merely presented to help illustrate the idea of the variations in shade, it being noted that the dashes constituting each example have a uniform pitch horizontally, while they vary in length to give the desired tone. It will also be understood that the received picture will comprise all of the various tones or shades which were found in the original picture and although the radio wave in transmission undergoes variations due to fading, the reproduced picture will be unaffected by such fading provided of course the received signal does not fall below the minimum for which the receiver will respond. By simply reversing connections at the transmitter 23, the transmitted picture may be made either a positive or a negative of the original picture as desired.

I have chosen the particular embodiments described above as illustrative of my invention, and it will be apparent that various other modifications may be made without departing from the spirit and scope of my invention, which modifications I aim to cover by the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

' 1. The method of transmitting shaded pictures by radio subject to fading whereby the pictures received are unaffected by said fading which comprises producing a carrier wave of constant frequency and amplitude,scanning a picture to be transmitted, producing thereby an alternating current of varying amplitude in accordance with the shade of the successive unit areas of the picture, rectifying said alternating current; keying said carrier wave in accordance with the amplitude of said rectified alternating current and transmitting said keyed carrier wave.

2. Apparatus for transmitting shaded pictures by means of radio whereby the received picture is unafiected by fading of the radio signal comprising means for producing a carrier wave having a fixed frequency and amplitude, means for scanning a picture to be transmitted, means for producing an auxiliary wave having a fixed frequency, means for varying the amplitude thereof in accordance with the shade of the successive unit areas of the picture being scanned, means for rectifying said auxiliary wave, means for keying said carrier wave in accordance with the times. during which the rectified auxiliary wave exceeds a predetermined value and means for transmitting the keyed carrier wave.

3. Apparatus for transmitting shaded picture comprising means for scanning the picture to form and an amplitude which varies in accordance with the shade of the successive unit areas of the picture being scanned, means for producing a carrier, and keying means for said carrier responsive to the intervals during which said wave exceeds a predetermined value.

5. The method of transmitting pictures which comprises scanning the picture to be transmitted,

producing a constant frequency alternating current having a concave wave form and having an amplitude which varies with the shade of the elemental areas of the picture being scanned, rectifying said current and transmitting signals at constant frequency intervals which vary in length with the amplitude of the rectified current.

6. The method of transmitting pictures which comprises scanning the picture to be transmitted, producing a constant frequency alternating current whose amplitude varies with the shade of the elemental areas of the picture being scanned,

DIS'CLAIMER 1,950,171.-'Pdtd O. Gardiner, Sootia, N. Y. Prc'rnan TRANSMISSION. Patent dated March 6, 1934. Disclaimer filed December 18, 1934, by the assignee,

1 General Electric Company.

Hereb; enters the following disclaimer: v claun 1 of the said Letters Patent aforesaid, the combination of the method steps 18 dlsclaimed except when an undulating currentfsimilar in wave form to the current produced by O Gazette January 15, 1935.]

, is derived from. the rectified alternating current.

3 {DISCLAIMER 1,950,1l 1.-Paul Gardiner, .Scotiti, N. Y. PICTURE Tnarrsirrsgron. Patent dated March 6, 1934. Disclaimer filed March 16, 1935, by the aseignee, General Electn'c Company.

Herebfi enters the following disclaimer to claim 1 of said Letters Patent which i is in the 0 owing words, to-wit:

The method of transmitting shaded pictures by radio subject to fading whereby the pictures received are unaffected b said fading which comprises producing a carrier wave of constant frequency an! amplitude scanning a lcture to be transmitted, producin thereby analternating current of varying amp 'tude in accordance with the shade o the successive unit areas of thepicture, rectifying said alternatin current, keying said carrier wave in accordance w1th the amplitude of said rectifie alternating current and transmitting said keyed carrier wave. 

